The circadian rhythm is a physiological phenomenon that fluctuates with a period of approximately 24 hours. The circadian rhythm is found in biological activity including brain waves, hormone secretion, and cellular regeneration, and it plays an important role in determining sleeping and eating patterns. Disturbance of circadian rhythm or reduction in circadian rhythm function causes various alterations such as sleep disorder, insomnia, autonomic imbalance and endocrine dysfunction.
It is in light of this that agents for improving circadian rhythm capable of restoring circadian rhythm disturbance or circadian rhythm function are thought to be useful. Patent literature 1, for example, discloses a functional composition that modulates circadian rhythm, comprising a lactic acid bacteria fermentate of soybean milk as an active ingredient. Also, patent literature 2 discloses an agent for improving circadian rhythm comprising whey as an active ingredient.